1. Field of the Invention
This invention relates to a medical apparatus which contains a first apparatus part and a second apparatus part which is movable with respect to the first part. In particular, this invention relates to a security device for such a medical apparatus. Still more particularly, this invention relates to an electron applicator for a linear accelerator, or the like.
2. Description of the Prior Art
It is well known to use safety devices with medical apparatus which protect the patient, the operating personnel and the apparatus itself. Such a safety device is especially important in a medical apparatus in which a part extends towards the patient. In such an apparatus there exists the hazard that the patient may move unexpectedly and may hurt himself or herself by hitting against the protruding part.
Thus, it is desirable to have a safety device working in conjunction with the protruding apparatus part so that the patient will not get hurt in case he or she should inadvertently move against the extruding part.
In the field of linear accelerators, electron applicators having such safety feature are widely used. An electron applicator used in a linear accelerator determined for radiotherapy of patients is known from U.S. Pat. No. 4,314,158. This electron applicator is essentially an assembly of an outer or support tube and an inner or insert tube. The support tube is stationary and connected to the collimator of the linear accelerator. The upper portion of the insert tube is slidably mounted inside the support tube. Both tubes are preferably of cylindrical shape. A safety device is provided for preventing the insert tube from sliding out of the support tube. This safety device also engages the insert tube in a first working position when a treatment is performed. The safety device comprises a spring loaded pin extending through a hole in the wall of the support tube into an annular groove which is provided in the outer surface of the end portion of the insert tube. Upon a predetermined axial force, which may be inadvertently exercised by the patient under treatment, the insert tube slides back into the support tube.
In this electron applicator the actual force that has to be overcome in an emergency situation is primarily determined by the radial holding force, by the size and by the shape of the spring loaded pin. In addition, the principle of this safety device necessarily requires two tubes whereby the inner tube is slidably mounted in the outer tube. These features may result in some design restrictions.